Semiconductor chips or dies typically are manufactured from a semiconductor material such as silicon, germanium, or gallium/arsenide. An integrated circuit or other active feature(s) is incorporated in the die adjacent one surface, often referred to as the “active surface,” of the die. The active surface typically also includes input and output terminals to facilitate electrical connection of the die with another microelectronic component.
Since semiconductor dies can be degraded by exposure to moisture and other chemical attack, most dies are encapsulated in a package that protects the dies from the surrounding environment. The packages typically include leads or other connection points that allow the encapsulated die to be electrically coupled to another electronic component, e.g., a printed circuit board. Typically, the leads extend laterally outwardly in a flat array that is part of a lead frame. Leaded packages include a semiconductor die, which may be attached to the lead frame either by seating the die on a die paddle or attaching the die directly to the leads, e.g., via a die attach adhesive in a leads-on-chip attachment. Some or all of the terminals of the semiconductor die then may be electrically be connected to leads of the lead frame, e.g., by wire bonding. The connected lead frame and die may then be encapsulated in a mold compound to complete the packaged microelectronic component assembly. The leads extend outwardly from the mold compound, allowing the features of the semiconductor die to be electrically accessed. Finally, the lead frame will be trimmed and formed into a desired configuration of electrically independent leads.
FIG. 1 schematically illustrates a conventional packaged microelectronic component assembly 10. This microelectronic component assembly 10 includes a semiconductor die 20 having an active surface, which bears an array of terminals 24, and a back surface 26. This microelectronic component assembly 10 is a conventional leads-on-chip package with a plurality of leads 30a and 30b attached to the active surface 22 of the die 20 by adhesive members 35a and 35b. Typically, the inner length 32a of each of a series of first leads 30a will be attached to a first adhesive member 35a. The inner length 32b of each of a set of second leads 30b are attached to the die 20 by a second adhesive member 35b. The inner ends of the first leads 30a may be spaced from the inner ends of the second leads 30b. This defines a terminal gap 34 between the ends of the leads 30 through which the terminals 24 of the die 20 can be accessed by a wire bonding machine or the like.
The microelectronic component assembly 10 also includes a plurality of bond wires 40. A first set of bond wires 40a may extend from individual terminals 24 of the die 20 to the inner ends 32a of the first leads 30a. Similarly, a series of second bond wires 40b may extend from other terminals 24 in the terminal array to the inner ends 32b of the second leads 30b. Typically, these bond wires 40 are attached using wire bonding machines that spool a length of wire through a capillary. A molten ball may be formed at a protruding end of the wire and the capillary may push this molten ball against one of the terminals 24, thereby attaching the terminal end 42 of the wire 40 to the die 20. The capillary will then be moved laterally in a direction away from the lead 30 to which the wire 40 will be attached (referred to as the reverse motion of the capillary) then a further length of the wire will be spooled out and the lead end 44 of the wire 40 will be attached to the inner end 32 of one of the leads 30. The reverse motion of the capillary is required to bend the wire into the desired shape to avoid undue stress at either the terminal end 42 or the lead end 44.
The need to move the capillary in the reverse direction to form the bend in the wire 40 requires significant clearance between the terminal end 42 and the inner ends of the leads 30. This increases the width W of the terminal gap 34. This, in turn, increases the length of each of the bond wires 40 and often requires an increased loop height L of the wire 40 outwardly from the active surface 22 of the die 20. By way of example, a conventional microelectronic component assembly 10 may include adhesive members 35 having a thickness of about 4 mils and a lead frame 30 having a lead frame of about 5 mils. In such a microelectronic component assembly 10, the width W of the terminal gap 34 commonly will be on the order of 100 mils (about 2.5 mm) or more. (FIG. 1 is merely a schematic illustration and is not drawn to scale; the thicknesses of many of the elements of the assembly 10 have been exaggerated for purposes of clarity.) Conventional wire bonding machines commonly yield a maximum loop height L in such an assembly 10 of about 10–14 mils.
As noted above, most commercial microelectronic component assemblies are packaged in a mold compound 50. The mold compound 50 typically encapsulates the die 20, the adhesive members 35, the bond wires 40, and the inner lengths 32 of the leads 30. A remainder of the leads 30 extends laterally outwardly from the sides of the mold compound 50. In many conventional applications, the mold compound 50 is delivered using transfer molding processes in which a molten dielectric compound is delivered under pressure to a mold cavity having the desired shape. In conventional side gate molds, the mold compound will flow from one side of the cavity to the opposite side. As the front of the molten dielectric compound flows along the terminal gap 34 under pressure, it will tend to deform the wires. This deformation, commonly referred to as “wire sweep,” can cause adjacent wires 40 to abut one another, creating an electrical short. Wire sweep may also cause one of the wires 40 to bridge two adjacent leads, creating an electrical short between the two leads. These problems become more pronounced as the wire pitch becomes smaller and as thinner wires 40 are used. For example, the stiffness of a 20 μm diameter wire is only about 40% that of a 25 μm wire and a 15 μm diameter wire is only about 13% as stiff as a 25 μm wire. Since semiconductor dies 20 are continually decreasing in size and the terminals 24 are getting closer and closer to one another, wire sweep in conventional packaged microelectronic component assemblies 10 is likely to cause even more problems in the future.